Fine-scale temporal control for laser material processing

ABSTRACT

Methods include directing a laser beam to a target along a scan path at a variable scan velocity and adjusting a digital modulation during movement of the laser beam along the scan path and in relation to the variable scan velocity so as to provide a fluence at the target within a predetermined fluence range along the scan path. Some methods include adjusting a width of the laser beam with a zoom beam expander. Apparatus include a laser source situated to emit a laser beam, a 3D scanner situated to receive the laser beam and to direct the laser beam along a scan path in a scanning plane at the target, and a laser source digital modulator coupled to the laser source so as to produce a fluence at the scanning plane along the scan path that is in a predetermined fluence range as the laser beam scan speed changes along the scan path.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/569,403, filed Sep. 12, 2019, which is a continuation of U.S. patentapplication Ser. No. 15/357,484, filed Nov. 21, 2016, now U.S. Pat. No.10,434,600, which claims the benefit of U.S. Provisional PatentApplication No. 62/292,108, filed Feb. 5, 2016, and U.S. ProvisionalPatent Application No. 62/258,774, filed Nov. 23, 2015, all of which areincorporated by reference herein in their entirety.

FIELD

The disclosure pertains to laser material processing.

BACKGROUND

In recent years, additive manufacturing and 3D printing techniques havegrown in popularity as the technology of forming objects with sequentiallayers has matured and become widely accessible. In particular, it maynow be possible for laser-based methods, such as selective laser melting(SLM) and selective laser sintering (SLS), to supplant traditionaltechniques for manufacturing industrial-grade objects, such as castingand machining. However, numerous obstacles remain. For example,conventional additive manufacturing methods are typically unable tocreate objects as quickly, or that are as reliable in their finishedstate, as their traditionally-manufactured counterparts. Furthermore,the created objects often do not have superior precision detail orfeature resolution. Accordingly, a need remains for innovation directedto solving the problems and drawbacks associated with conventionaladditive manufacturing apparatus and methods.

SUMMARY

According to some embodiments, methods comprise directing a laser beamto a target along a scan path at a variable scan velocity, and adjustinga digital modulation during movement of the laser beam along the scanpath and in relation to the variable scan velocity so as to provide afluence at the target within a predetermined fluence range along thescan path.

According to further embodiments, methods comprise directing a laserbeam to a target along a scan path which includes adjusting a width ofthe laser beam with a zoom beam expander so as to provide the laser beamwith a variable spot size at the target, receiving the laser beam fromthe zoom beam expander by a 3D scanning system having a z-axis focusadjust optical system and a galvanometer scanning system, and scanningthe laser beam with the variable spot size along the scan path at thetarget.

According to further embodiments, apparatus comprise a laser sourcesituated to emit a laser beam, a 3D scanner situated to receive thelaser beam and to direct the laser beam along a scan path in a scanningplane at the target, and a laser source digital modulator coupled to thelaser source so as to produce a fluence at the scanning plane along thescan path that is in a predetermined fluence range as the laser beamscan speed changes along the scan path. In additional examples,apparatus further comprise a zoom beam expander situated to receive thelaser beam from the laser source and to change a width of the laser beamreceived by the 3D scanner so as to change a size of a focused laserspot of the laser beam in the scanning plane.

According to additional embodiments, methods comprise focusing a laserbeam at a target within a focus field, scanning the focused laser beamat a variable speed along a scan path, and digitally modulating thelaser beam during the scan movement along the scan path so as to adjusta laser beam average power received by the target along the scan pathand so as to provide the target with a fluence that is above or belowone or more laser process thresholds associated with the target.

According to further examples, methods comprise directing a laser beamto a target along a scan path at a variable scan velocity, and adjustinga collimated width of the laser beam with a zoom beam expander based onthe variable scan velocity. In some examples, the collimated width isadjusted so as to provide the laser beam with a variable spot size atthe target and a fluence at the target within a predetermined fluencerange along the scan path. Some examples can further comprise adjustinga digital modulation of the laser beam based on the variable scanvelocity.

In additional embodiments, methods comprise adjusting a width of a laserbeam with a zoom beam expander so as to provide the laser beam with avariable spot size at a target, directing the laser beam to the targetalong a scan path, and a digitally modulating the laser beam in relationto the variable spot size so as to provide a fluence at the targetwithin a predetermined fluence range along the scan path. In furtherexamples, the laser beam is directed to the target along a scan path ata variable scan speed and the digital modulation is adjusted so as tomaintain the fluence at the target within the predetermined fluencerange along the scan path.

The foregoing and other objects, features, and advantages of thedisclosed technology will become more apparent from the followingdetailed description, which proceeds with reference to the accompanyingfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side view schematic of an additive manufacturingapparatus.

FIG. 2A shows a top view of a laser patterning scan path.

FIGS. 2B-2I show graphs of variables related to a scanned laser beam.

FIG. 3 is a graph of fluence with respect to focus position.

FIG. 4 shows a side view schematic of a laser patterning apparatus.

FIG. 5 shows another side schematic of a laser patterning apparatus.

FIG. 6 is a flowchart of a laser patterning process.

FIG. 7 is a schematic of a laser patterning system.

FIG. 8 is another schematic of a laser patterning system.

FIG. 9 is another schematic of a laser patterning system.

DETAILED DESCRIPTION

As used in this application and in the claims, the singular forms “a,”“an,” and “the” include the plural forms unless the context clearlydictates otherwise. Additionally, the term “includes” means “comprises.”Further, the term “coupled” does not exclude the presence ofintermediate elements between the coupled items.

The systems, apparatus, and methods described herein should not beconstrued as limiting in any way. Instead, the present disclosure isdirected toward all novel and non-obvious features and aspects of thevarious disclosed embodiments, alone and in various combinations andsub-combinations with one another. The disclosed systems, methods, andapparatus are not limited to any specific aspect or feature orcombinations thereof, nor do the disclosed systems, methods, andapparatus require that any one or more specific advantages be present orproblems be solved. Any theories of operation are to facilitateexplanation, but the disclosed systems, methods, and apparatus are notlimited to such theories of operation.

Although the operations of some of the disclosed methods are describedin a particular, sequential order for convenient presentation, it shouldbe understood that this manner of description encompasses rearrangement,unless a particular ordering is required by specific language set forthbelow. For example, operations described sequentially may in some casesbe rearranged or performed concurrently. Moreover, for the sake ofsimplicity, the attached figures may not show the various ways in whichthe disclosed systems, methods, and apparatus can be used in conjunctionwith other systems, methods, and apparatus. Additionally, thedescription sometimes uses terms like “produce” and “provide” todescribe the disclosed methods. These terms are high-level abstractionsof the actual operations that are performed. The actual operations thatcorrespond to these terms will vary depending on the particularimplementation and are readily discernible by one of ordinary skill inthe art.

In some examples, values, procedures, or apparatus' are referred to as“lowest”, “best”, “minimum,” or the like. It will be appreciated thatsuch descriptions are intended to indicate that a selection among manyused functional alternatives can be made, and such selections need notbe better, smaller, or otherwise preferable to other selections.

As used herein, laser beams and associated optical radiation refers toelectromagnetic radiation at wavelengths of between about 100 nm and 10μm, and typically between about 500 nm and 2 μm. Examples based onavailable laser diode sources and optical fibers generally areassociated with wavelengths of between about 800 nm and 1700 nm. In someexamples, propagating optical radiation is referred to as one or morebeams having diameters, asymmetric fast and slow axes, beamcross-sectional areas, and beam divergences that can depend on beamwavelength and the optical systems used for beam shaping. Forconvenience, optical radiation is referred to as light in some examples,and need not be at visible wavelengths.

Representative embodiments are described with reference to opticalfibers, but other types of optical waveguides can be used having square,rectangular, polygonal, oval, elliptical or other cross-sections.Optical fibers are typically formed of silica (glass) that is doped (orundoped) so as to provide predetermined refractive indices or refractiveindex differences. In some, examples, fibers or other waveguides aremade of other materials such as fluorozirconates, fluoroaluminates,fluoride or phosphate glasses, chalcogenide glasses, or crystallinematerials such as sapphire, depending on wavelengths of interest.Refractive indices of silica and fluoride glasses are typically about1.5, but refractive indices of other materials such as chalcogenides canbe 3 or more. In still other examples, optical fibers can be formed inpart of plastics. In typical examples, a doped waveguide core such as afiber core provides optical gain in response to pumping, and core andcladdings are approximately concentric. In other examples, one or moreof the core and claddings are decentered, and in some examples, core andcladding orientation and/or displacement vary along a waveguide length.

In the examples disclosed herein, a waveguide core such as an opticalfiber core is doped with a rare earth element such as Nd, Yb, Ho, Er, orother active dopants or combinations thereof. Such actively doped corescan provide optical gain in response to optical or other pumping. Asdisclosed below, waveguides having such active dopants can be used toform optical amplifiers, or, if provided with suitable optical feedbacksuch as reflective layers, mirrors, Bragg gratings, or other feedbackmechanisms, such waveguides can generate laser emissions. Optical pumpradiation can be arranged to co-propagate and/or counter-propagate inthe waveguide with respect to a propagation direction of an emittedlaser beam or an amplified beam.

The term brightness is used herein to refer to optical beam power perunit area per solid angle. In some examples, optical beam power isprovided with one or more laser diodes that produce beams whose solidangles are proportional to beam wavelength and beam area. Selection ofbeam area and beam solid angle can produce pump beams that coupleselected pump beam powers into one or more core or cladding layers ofdouble, triple, or other multi-clad optical fibers. The term fluence isused herein to refer energy per unit area. In some embodiments, fluenceis delivered to a target in along a scan path so as to heat or otherwiselaser process the target in a selected area associated with the scanpath. Scan paths can have various shapes, including linear, curved,retraced, segmented, etc. Output beams generated by optical systems aredirected along the scan paths and can have various brightnesses anduniformity characteristics along one or more axes transverse to thepropagation direction. Typical output beams are continuous-wave withvarious output powers, including average beam powers greater than orequal to 100 W, 500 W, 1 kW, 3 kW, 6 kW, 10 kW, or 20 kW, depending onthe particular application. Continuous-wave output beams are digitallymodulated as discussed further herein.

FIG. 1 is an apparatus 100 that includes a laser system 102 emitting anddirecting a laser processing beam 104 to a target 106 in an additivemanufacturing process. The target 106 is generally formed layer by layerfrom a fine metal powder 108 that is situated in a container 110. Once alayer is laser patterned, a z-stage 112 lowers the container 110 and anew layer of fine metal powder 108 is rolled out with a roller 114 thatprovides additional fine metal powder 108 from an adjacent reservoir116. The new layer is then laser patterned, and the process is repeatedmultiple times with subsequent fine metal powder layers in order to forma three dimensional object.

In FIG. 2A an example of a scan path 200 is shown along which a laserprocessing beam is scanned in the process of laser patterning a target,such as an additive manufacturing target. At a time t₁, the laserprocessing beam is traveling with scan velocity, e.g., a particularspeed and a direction to the right in the plane of FIG. 2A. The scanspeed of the laser processing beam begins to slow as the laserprocessing beam reaches another position at a time t₂ closer to a pathcorner. At a time t₃, the laser processing beam slows to becomemomentarily motionless in order to change direction and move downward inthe plane of FIG. 2A. At a time t₄, the scan speed of the laserprocessing beam has increased, and at time t₅ the laser processing beamhas reached the same speed as at time t₁.

Below the scan path 200, FIG. 2B shows a graph 202 of speed, |v(t)|,versus time that corresponds with the times t₁-t₅ of the scan path 200.As can be seen, a speed of the laser processing beam has an initial scanspeed at t₁, slows to rest at time t₃ where the laser processing beamchanges direction, and increases scan speed to a final scan speed at t₅that can be the same or different from the initial scan speed. Below thegraph 202, in FIG. 2C, is a graph 204 of a laser processing beam averagepower P_(AVG)(t) versus time corresponding with the times t₁-t₅ and thescan path 200, and in FIG. 2D, a graph 206 of fluence E(x) received by aprocessing target along a scan path, such as the scan path 200. Intypical laser process examples, the fluence E(x) should remain within apredetermined range, such as between two thresholds, such as constantthresholds F_(HIGH), F_(LOW). In some examples, the thresholds andcorresponding predetermined range can vary or be modulated depending onvarious factors, such as feature size and shape, material-dependentcharacteristics, such as heating and cooling rates, etc. For example,different targets, or different portions or regions of the same target,can have different material properties. Also, different laser processingeffects can be achieved in different process windows, including fluencewindows. By maintaining fluence within a corresponding range or ranges,the laser energy can perform the desired change to the target. Forexample, in a selective laser melting process an excess fluence maydamage the target, exacerbating a heat affected zone, and negativelyaffect various parameters of the finished object, such as tensilestrength and reliability. An insufficient fluence can prevent the targetmaterial from melting correctly thereby weakening the finished object.By maintaining fluence within a predetermined range during laserprocessing, the finished object can be fabricated with superior materialcharacteristics.

In some embodiments, in order to maintain fluence E(x) within thepredetermined range (e.g., between F_(HIGH) and F_(LOW)), the averagepower P_(AVG)(t) of the laser processing beam decreases corresponding tobeam movement information, such as a decrease in scanning speed |v(t)|of the laser processing beam along the scan path 200. However, forvarious reasons, a direct continuous decrease in average powerP_(AVG)(t) cannot be accomplished or cannot be accomplished in anefficient manner. For example, the laser scanning components, such asmirrors and optics, can move at a speed slower than the laser patterningprocess demands, resulting in a laser fluence at the target that isabove F_(HIGH) or below F_(LOW). In some instances, the dynamics of again medium of a laser source generating the laser processing beam donot respond quickly enough to a desired continuous or discontinuouschange to the power level of the laser processing beam.

Below the graph 206, in FIG. 2E, is a graph 208 depicting a modulatedpower P(t) of the laser processing beam that can produce rapid changesin average power P_(AVG)(t) even with slow scanner dynamics or otherlaser system deficiencies. The modulated power P(t) alternates between ahigh power P_(HIGH) and a low power P_(LOW), and the low power P_(LOW)can be zero or non-zero. The modulated power P(t) includes a variablemodulation period T_(MOD) and a variable duty cycle P_(DUTY) that is apercentage of T_(MOD). In general, as a speed associated with thescanning of a laser processing beam decreases, one or more of themodulation period T_(MOD) and duty cycle P_(DUTY) can change so as todecrease the average power of the laser processing beam and to maintainthe fluence received by the target within a predetermined range. In someexamples, other information associated with the scan path 200 is used tomaintain fluence E(x) within the predetermined range, such as proximityof the scan path 200 to an adjacent portion of the scan path 200previously scanned (including a retrace), ambient temperature, localizedtemperature, heating and cooling rates, scan acceleration, scanposition, etc. In further examples, a delivered fluence and a peak powerof the laser beam delivering the fluence remain within predeterminedranges in accordance with laser process requirements. In particularembodiments, fine features (on the order of microns) are laser processedas laser processing beam scan velocity changes rapidly during theformation of smaller target details. In some embodiments, the modulationperiod T_(MOD) can be varied so that an average beam power changes basedon response dynamics of a gain medium of a laser source generating thebeam or other components of the laser source.

In the example shown in graph 208, at the time t₁ the power of the laserprocessing beam is constant at power P_(HIGH). As the speed |v(t)| ofthe laser processing beam decreases, the laser processing beam changesfrom constant power to a modulated power, switching from P_(HIGH) toP_(LOW) and back to P_(HIGH) at a frequency associated with the decreasein scanning speed of the laser processing beam. As the speed |v(t)| ofthe scanning of the laser processing beam continues to decrease as thetime approaches t₂ and t₃, the power modulation frequency increases,decreasing the period T_(MOD) and the duty cycleT_(HIGH)/T_(HIGH)+T_(LOW), wherein T_(HIGH) is a duration during whichthe power P_(HIGH) is applied and T_(LOW) is a duration in which thepower P_(LOW) is applied. The decreased duty cycle reduces the averagepower P_(AVG) for the laser processing beam and provides the laserprocessing fluence within the predetermined range. Thus, by adjusting adigital modulation of the power of the laser processing beam, theaverage power of the laser processing beam can be adjusted so that afluence may be provided at target that remains within a predeterminedfluence range corresponding to the target. With additional reference tograph 210 in FIG. 2F, in some embodiments, the laser processing beam canchange to or switch between more than two power levels, such as P0, P1,and P2, and digitally modulated to produce rapid changes in averagepower and associated fluence. In further examples, a decrease in averagelaser processing beam power can be provided by adjusting a digitalmodulation of the laser processing beam such that a power level iswithin a range of peak powers suitable for performing a laser process.

As discussed above, predetermined fluence ranges can vary according tolaser processing factors, and examples herein can produce modulatedoptical beam powers that maintain fluence within variable fluenceranges. FIG. 2G shows a graph 212 of fluence E_(STEP) with a targetedfluence that varies step-wise from a first fluence F₁ with thresholdsF_(1-HIGH), F_(1-LOW) to a second fluence F₂ with thresholds F_(2-HIGH),F_(2-LOW). In some examples, with a constant scan velocity for a laserprocessing beam, such as with a straight scan path, a digitallymodulated beam with a fixed period and duty cycle can provide the firstfluence F₁ and an unmodulated beam can provide the second fluence F₂.Digital modulation of the power can allow for more a rapid transitionbetween the first and second fluences F₁, F₂. In FIG. 2H, a graph 214shows a predetermined fluence range F_(MOD) that varies according to asinusoid between respective upper and lower fluence boundaries F_(HIGH),F_(LOW). The fluence E_(ACTUAL) delivered to a target can be maintainedwithin the fluence range F_(MOD) through a digital modulation of theoptical power of the laser processing beam. In some laser processingexamples, the frequency of the fluence modulation can be relativelyfast, including 1 kHz, 10 kHz, 100 kHz, or greater. In differentexamples, high frequency fluence oscillation is dependent on orindependent from a fluence oscillation phase.

In some examples, an analog modulation can be applied to change theaverage power of the laser processing beam in conjunction with thedigital modulation. However, the analog modulation typically has aslower response time for achieving a desired reduction in average powerfor maintaining fluence within the predetermined range. To increaseprocess efficiency, and to robustly maintain fluence within apredetermined fluence range irrespective of various system variablessuch as scanner dynamics, a digital modulation is typically used or ahybrid digital and analog modulation is used to adjust the average powerof the laser processing beam and provide more rapid response to preservefluence within a predetermined range. For example, referring to FIG. 2I,a graph 216 shows a digitally modulated signal P_(MOD) that includesplurality of modulation portions with power maximums that decrease to aminimum power P_(LOW1) according to an analog command signal P_(ANALOG).The actual average output power commanded and produced for the laserprocessing beam can include trace a path P_(AVG) that can include a morerapid change in average beam power and a lower minimum power P_(LOW2).

FIG. 3. is a graph of fluence F(z) of a laser processing beam withrespect to a focus position Z associated a scanner coupled to the laserprocessing beam. In general, the fluence F(z) is a maximum at a fluenceF_(MAX) where the laser processing beam is brought into a best focusposition Z_(BEST) in the direction of propagation of the laserprocessing beam. As the focus distance of the laser processing beamincreases or decreases from Z_(BEST), effectively defocusing the laserprocessing beam, the fluence associated with the new focus positiondecreases as the laser processing beam expands and defocuses. Duringlaser processing it is generally desirable for the fluence F(z) of thelaser processing beam to remain within fluence boundaries F_(HIGH) andF_(LOW) by constraining or controlling defocus between focus positionsZ_(LOW) and Z_(HIGH), for example, so that the laser process can producethe corresponding change in the target. While the fluence boundaries canbe variable, in typical examples the fluence boundaries are fixed. Insome embodiments, a 3D scanner is used to scan the laser processing beamat the target with a flatter focal field curvature than an Fθ lens orother scanning optic over a large pattern processing area. Thus, thefluence delivered by the laser processing beam that is scanned at thetarget is more likely to stay or more easily maintained within thefluence boundaries F_(HIGH), F_(LOW).

In FIG. 4, an apparatus 400 includes a laser source 402 situated to emita laser processing beam 404. A laser controller 406 is coupled to thelaser source 402 in order to control the power, including a modulatedpower, of the laser processing beam 404. A 3D scanner 408 is situated toreceive the laser processing beam 404 and to direct the laser processingbeam to a target 410. With the 3D scanner 408, the laser processing beam404 is generally brought to focus in a focal plane 412 that is parallelto and aligned with a flat surface of the target 410. However, in someexamples, the 3D scanner 408 allows the focal position to vary so as toprovide a non-flat focal field that can correspond to a non-uniformtarget surface. In typical examples, the 3D scanner 408 includes an XYgalvanometer scan mirror set and a Z-position focus group that changesthe focus position of the of the beam at the focal plane 412 based onthe position of the galvo scan mirrors. The apparatus 400 also includesa zoom beam expander 414 situated to receive the laser processing beam404 with a collimated input diameter Do and adjust beam width so thatthe laser processing beam exiting the zoom beam expander 414 has a sameor different collimated diameter D₁ along one or more directionstransverse to the propagation path of the laser processing beam. Thelaser processing beam 404 with the collimated diameter D₁ is received bythe 3D scanner 408 and is scanned and focused at the target 410 with aspot size W₁. The zoom beam expander 414 can also adjust the laserprocessing beam 404 so as to have a collimated diameter D₂ that issmaller than the collimated diameter D₁. The smaller collimated diameterD₂ is received by the 3D scanner and scanned and focused at the targetwith a spot size W₂ that is larger than spot size W₁ due to the smallercollimated diameter D₂.

The zoom beam expander 414 can be constructed in various ways. Intypical examples (and as shown in FIG. 4), the zoom beam expander 414includes a set of entrance group optics 416 that are fixed and situatedto receive the laser processing beam 404 from the laser source 402. Aset of exit group optics 418 is situated to receive an expanding beamfrom the entrance group optics 416 and through movement along an opticalaxis of one or more optics of the exit group optics 418, increase ordecrease the diameter of the laser processing beam 404 emitted from thezoom beam expander 414. To provide the controlled movement for changingthe collimated diameter of the laser processing beam 404, the zoom beamexpander 414 is coupled to the laser controller 406. By controllablyexpanding the diameter of the laser processing beam 404 that isoptically coupled into the 3D scanner 408, a controlled variation inspot size can be provided at the target for various effects.

In typical examples, different spot sizes produced with the zoom beamexpander 414 are used to laser process features at the target 410 ofvarying size and shape. In some examples, the laser processing beam 404is scanned with a variable scan velocity along a scan path at the target410 so that the target receives a fluence in a predetermined fluencerange by varying the spot size in relation to the variable scanvelocity. In further examples, larger features are laser processed withthe laser processing beam 404 with a larger spot size, e.g., with thespot size W₂ and a constant laser processing beam power, and smallerfeatures are laser processed with the laser processing beam 404 with asmaller spot size, e.g., with the smaller spot size W₁ and a typicallysmaller digitally modulated laser processing beam power. By digitallymodulating the laser processing beam power, the laser process can avoidor make optional an analog modulation of the beam power and the fluencedelivered to the target can be maintained within a predetermined fluencerange for the laser process as changes in spot size occur.

FIG. 5 shows another apparatus 500 that includes a laser source 502controlled by a laser controller 504 and situated to produce acollimated laser beam 506. A zoom beam expander 508 is situated toreceive and to change the diameter of the collimated laser beam 506 toproduce an expanded beam 507. A 3D scanner 510 is situated to receivethe expanded beam 507 from the zoom beam expander 508 and to focus theexpanded beam 507 to a spot in various positions, S₁-S₃, at a target512. The 3D scanner 510 typically includes variable position focusingoptics 514 that receive and focus the expanded beam 507 and a pair ofgalvo-controlled scan mirrors 516 that receive the focused beam anddirect the focused beam to a particular position (typically in a focalplane) aligned with the target 512, e.g., to predetermined X-Ycoordinates. The position of the laser beam spot at the target 512 canvary across a scan field associated with the 3D scanner 510. In ascanner that uses a fixed focusing optic, such as an Fθ lens, a fieldcurvature 518 associated with the focal position of the Fθ lens istypically curved. Thus, for a laser beam focused at a position SN towarda periphery of the scan field, such as positions S₁ and S₃, defocustypically occurs. Such defocus can reduce the fluence received by thetarget 512 so that the fluence is outside of a predetermined range anduneven heating and uneven processing across the scan field can occur.The variable position focusing optics 514 (which can include one or morelenses, mirrors, diffractive optical elements, etc.) of the 3D scanner510 allows a change in a focus position of the spot in relation to anX-Y position of the spot in the field of the 3D scanner 510. Thus, smalladjustments can be made to the focus position of the spot so that fieldcurvature associated with 3D scanner is flatter than other systems. The3D scanner 510 is coupled to the laser controller 504 so as to receive ascanning and focusing signal that corresponds to pattern data forscanning and focusing the collimated laser beam 506 at the target. Thepattern data can be stored in the laser controller 504 or can bereceived from an external source.

In FIG. 6, a method 600 of laser processing a target includes, at 602,providing a scan path for a laser beam, and at 604, selecting a spotsize for the laser beam at the target. For example, a laser beam scanpath can be provided to a laser controller with a laser pattern filethat includes data related to the position of the laser beam that is tobe scanned across the target. The laser beam scan path can also beprovided to the laser controller in real time so that receipt of a scanpath signal by the laser controller or laser scanner occurs simultaneouswith or in close temporal relation to the scanning of the laser beam atthe target. At 606, an average power of the laser beam is determinedbased on the laser beam scan path and the laser beam spot size and alaser beam fluence range associated with laser processing of the target.The power of the laser beam is digitally modulated at 608 throughdigital modulation of one or more laser pump sources coupled to anactive medium that produces the laser beam. The digitally modulatedlaser beam corresponds to the determined average power at 606, which canchange significantly based on the scan path and spot size. At 610, thelaser beam is directed along the scan path provided at 602. In furtherexamples, an average power is determined for a scan path and the spotsize of the laser beam is varied to correspond to the determined averagepower. In further examples, both digital modulation and a variable spotsize are used to provide an average power to correspond to apredetermined fluence range.

In FIG. 7, a laser system 700 is situated to laser pattern a target 702with precision control of fluence at the target 702. The laser system700 includes a laser controller 704 coupled to a pump driver 706, suchas a voltage controlled AC/DC power supply or a voltage regulatorcoupled to a power supply, and laser scanner 708. The pump driver 706drives pump diodes 710 based on one or more of a voltage and current.The pump diodes 710 are coupled to a laser gain medium, such as anactive fiber 712, which uses the energy from the pump diodes 710 togenerate a laser system beam 714. The laser system beam 714 is receivedby a zoom beam expander 716 that can change the collimated width of thelaser system beam 714 exiting the zoom beam expander 716 in order tochange the size of a focused spot of the laser system beam 714 in thesame plane at the target 702 along one or more axes transverse to apropagation direction of the laser system beam 714. The laser scanner708 receives the laser system beam 714 from the zoom beam expander 716with a selected collimated beam width and directs the laser system beam716 to the target 702 in order to process a pattern and deposit along ascan path 715 a laser fluence within a predetermined range associatedwith a laser process.

In some examples, the laser controller 704 is coupled to a gate signal718 that provides the controller 704 with first state and second stateconditions for the laser system beam 714 and that can be associated withthe pattern formed on the target 702. For example, the gate signal 718can correspond to a laser patterning data file 720 that provides on andoff conditions so that as the laser system beam 714 is scanned, variousfeatures can be isolated or spaced apart from other features on thetarget 702 and complex features can be formed. The laser controller 704includes a gate control 722 that communicates a gate control signal tothe pump driver 706 so that the pump diodes 710 are energized to pumpthe active fiber 712 so as to correspond to the on and off associatedwith the gate signal. The laser patterning data file 720 can alsoprovide various vector data, such as scan position data, for the lasersystem beam 714 to be scanned at the target 702. The laser controller704 is coupled to the laser scanner 708, though in other examples thelaser patterning data file 720 can be coupled directly to the laserscanner 708. Various connections can be wired or wireless, and file datacan be stored in volatile or non-volatile memory. In further examples,the gate commands of the gate signal are stored in a memory of the lasercontroller 704.

In order to maintain laser fluence delivered to the target 702 within apredetermined range, the laser controller 704 includes fluence setpoint724 coupled to a modulation period control 726, a duty-cycle modulationcontrol 728, and an analog modulation frequency control 730, that arealso coupled to the pump driver 706. The modulation period control 726is situated to adjust a digital modulation period of the pump diodes710. For example, the optical power output of the pump diodes canincrease from a slower frequency and corresponding period to a fasterfrequency (e.g., from 10 kHz to 100 kHz, 200 kHz, or faster) andcorresponding period or from a continuous on-state (e.g., 0 kHz) so thata power associated with the laser system beam 714 alternates oralternates more rapidly between two or more power levels (e.g., 10 kHzalternating between 10 W and 500 W).

The duty cycle control 728 is situated to adjust a power duty cycle ofthe pump diodes 710. Duty cycles can range from greater than 90% to lessthan 10% and can vary in relation to the modulation period. Selectedduty cycles are typically large enough so that a suitable amount oflaser processing beam energy may be generated in relation to the riseand fall times of the laser processing beam of a selected modulationperiod so as to maintain laser processing beam average power at adesired level. In some examples, a fixed modulation period is selectedand a duty cycle is varied from 100% to less than 10% so as to produce acorresponding reduction in laser processing beam average power. Infurther examples, a modulation period decreases and a duty cycledecreases to correspond to a reduction in laser processing beam averagepower so that fine details associated with changes in scan velocity canbe formed with the laser processing beam.

The modulation period control 726 and the duty cycle control 728 canproduce a modulation change based on the fluence setpoint 724 in orderto decrease or vary an average power of the laser system beam 714 at thetarget. In some embodiments, the decrease in average power can beassociated with a decrease in the size of the spot of the laser systembeam 714 at the target 702 or a change in beam scan velocity, such as adecrease in scan speed or change in scan direction, of the laser systembeam 714 being scanned with respect to the target 702. The power of thelaser system beam 714 can be detected by a power detector 732 coupled toone or more system components, such as the active fiber 712, with acorresponding signal of the detected power being coupled to thecontroller 704. The detected power of the laser system beam 714 can beused for general monitoring, emergency cutoff, etc., and also to assistin determining whether laser fluence remains within, above, or below oneor more thresholds, boundaries, tolerances, etc., during laserprocessing. For example, the detected power can be compared with anaverage power calculated based on a particular digital modulationsettings and the modulation period control 726 and duty cycle control728 can scale or adjust modulation period and duty cycle to produce thelaser system beam 714 with an average power that corresponds with thefluence setpoint 724. For example, the laser system 700 can be coupledto different types of laser scanners, pump diodes, active fibers, etc.,each which could affect dynamics of the laser system 700 and the extentto which digital modulation adjustment affects fluence deposition.

In some examples, a digital modulation period and duty cycle that areadjusted based on the fluence setpoint 724 can be defined by the gatesignal 718 prior to the coupling of the gate signal 718 to the lasercontroller 704. In further embodiments, the pattern file 720 can becoupled to the controller 704 and the gate signal 722 need not beexternally provided. In additional embodiments, the analog modulationcontrol 730 also is used to assist in maintaining laser fluence at thetarget 702 by combining it with the modulation period control 726 andthe duty cycle control 728. Typically, the analog modulation of theoutput power of the laser system beam 714 alone responds too slowly tomaintain the delivered laser fluence at the target 702 within thepredetermined range associated with the fluence setpoint 724 or thefluence requirements of the laser process. Typically, this inability canbe associated with dynamics of the electronics of the controller 704 orthe pump diodes 710 and active fiber 712. However, dynamics of the zoombeam expander 716 and the laser scanner 708 can also vary. Thus, byusing the modulation period control 726 and the duty cycle control 728to digitally modulate the pump diodes 710, laser fluence delivered tothe target 702 can be maintained within a predetermined range even withslow or inconsistent dynamics between various components of the lasersystem 700. In some examples, the combined effect on laser fluence fromthe modulation period control 726, duty cycle control 328, and theanalog modulation control 730 can advantageously maintain fluence atdesired levels.

In further examples, the modulation period control 726 can also adjustmodulation period based on the pattern file 720 or other data associatedwith the laser scan path 715. In patterns associated with the target 702where fine features are produced, such as multiple features in proximityto each other, the total heat load can affect laser process fluencethresholds for adjacent or retraced features. Modulation period control726 and duty cycle control 728 can adjust power of the laser system beam714 based on a delivered heat load to the target 702, a predicted ormeasured temperature associated with one or more portions of the target702, or the dwell time of the laser system beam 714 in one or more areasof the target 702, etc. For example, the laser system beam 714 can bedigitally modulated through a first scan movement change relative to thetarget 702 (e.g., a first turn of the laser system beam 714) in thelaser scan path 715 and can be digitally modulated to reduce an averagepower of the laser system 714 to a greater extent during a second turnin proximity to the first turn.

In FIG. 8, a laser system 800 includes a controller 802 situated toreceive an analog signal at an analog input 804, a gate signal at a gateinput 806, and a fluence modulation signal at a fluence modulation input808. The controller 802 typically uses the gate signal to modulate orvary power provided by a power supply 810 to laser pump diodes 812,typically by varying drive currents supplied to the laser pump diodes812. The laser pump diodes 812 are optically coupled to a doped fiber814, or other laser gain medium that generates a laser system beam 816.The power of the laser system beam 816 can increase and/or decreasecorresponding to the modulation of the gate signal, for example, so asto decrease between processing non-contiguous portions of a selectivelaser melting (SLM) target 818. A rise-fall circuit 820 is coupled tothe controller 802 and the pump diodes 812 to control a rise time and afall time of a pump current provided to the pump diodes 812 by the powersupply 810. By controlling the rise time and fall time of the pumpcurrent, associated rise times, fall times, overshoots, and undershootsof one or more pump beams 822 generated by the pump diodes 812 can beselected. In some examples, suitable response times for the pump beams822 can be balanced against pump diode reliability. The laser systembeam 816 generated by the doped fiber 814 is also coupled to a zoom beamexpander 824 situated to change the spot size of the laser system beam814 that is focused through a laser scanner 826 into the same plane atthe SLM target 818. Rise times are typically defined as the durationrequired for a parameter, such as laser beam power, to rise from aselected portion of a steady state value to another selected portion ofthe steady state value, e.g., 2% and 98%, 5% and 95%, 10% and 90%, 1%and 95%, etc. Fall times can be similarly defined as a duration for afall from a steady state value. Initial values or steady state fallvalues can be zero or non-zero. Overshoots and undershoots can bedefined as a percentage of a steady state value.

The fluence modulation signal can also be used to modulate, vary, orcontrol the laser system beam power to the same or different powerlevels associated with the gate signal. The fluence modulation signalcan be used to digitally modulate the pump currents of the pump diodes812 so that an average power of the laser system beam 816 is variedcorresponding to a variable velocity of the laser system beam 816 beingscanned by the laser scanner 826 at the SLM target 818. For example, adecrease in digital modulation period or a reduction in duty-cycle forthe same period can cause a rapid reduction in average power of thelaser system beam 816. The variable velocity of the laser system beam816 scanning along the scan path, or the change in spot size of thelaser system beam 816 with the beam expander 824, can produce anundesirable fluence variation at the SLM target 818 that can adverselyaffect the suitability of the finished product, and the fluencemodulation signal can be used to compensate for the fluence variation.The fluence modulation signal can also be used to digitally modulate thepump currents to adjust a power of the laser system beam 816 tocorrespond to different spot sizes produced by the zoom beam expander824. In some embodiments, the fluence modulation signal and the gatesignal can be provided through a common input. In further embodiments,the fluence modulation signal can be used to modulate or vary the spotsize of the laser system beam 814 with the zoom beam expander 824 so asto adjust the average power of the laser system beam 814. For example,the spot size can be varied to different sizes that correspond to thevariation of the scan velocity of the laser system beam 816. Also, thespot size can be modulated so as to alternate between two or moredifferent sizes, with different modulation periods and duty cycles, soas to alter the average power of the laser system beam 816.

FIG. 9 shows a laser pump control system 900 that controls the opticaloutputs 901A, 901B of one or more pump diodes 902A, 902B (typicallyseveral) situated in series in one or more pump modules 904. The opticaloutputs 901A, 901B can be used to directly produce a laser systemprocessing beam in a laser system, such as in so-called direct-diodelaser systems, or to pump other gain media to produce a laser systemprocessing beam (e.g., fiber lasers, solid state lasers, disk lasers,etc.). An AC/DC power supply 906 provides a current to the pump diodes902A, 902B in order to produce the optical outputs 901A, 901B. An FPGA908, or other similar controller device (e.g., PLC, PLD, CPLD, PAL,ASIC, etc.), is situated to produce a digital output 909 to a DAC 910that corresponds to a desired pump current for the pump diodes 902A,902B so as to generate the corresponding pump diode optical outputs901A, 901B. The DAC 910 converts the digital output from the FPGA into aDAC output 911A having a corresponding voltage and that is received bythe AC/DC power supply 906 to generate the pump current.

A plurality of additional DAC outputs, 911B-911D, are coupled to asignal multiplexer 912 situated to select the rise time and fall time ofthe pump current received by the pump diodes 902A, 902B. The signalmultiplexer 912 is coupled to an RC circuit capacitor C and one or morecurrent control circuits 914 situated to control the pump current thatgenerates the optical outputs 901A, 901B from the pump diodes 902A,902B. For example, a resistor R_(B) coupled to DAC output 911B can beassociated with a longer pump current rise time for the pump diodes902A, 902B, a resistor R_(C) can be associated with a shorter pumpcurrent rise time, and resistor R_(D) can be associated with a suitablepump current fall time. Rise times and fall times are typicallyasymmetric in the pump diodes 902A, 902B so that having differentselectable resistance values associated with rise and fall and producean improved response, such as a shorter rise time and fall time with aconstrained overshoot or undershoot. In some examples, adjustableresistors are used, such as digipots, so as to allow a tunableresistance value that can also vary with a digital modulation andproduce improved rise time, fall time, overshoot, and undershoot opticalresponse characteristics. A serial bus 916 can communicate a digitalmodulation command from the FPGA 908 to the multiplexer 912 so as toswitch between different rise times and fall times and to digitallymodulate the pump current.

The current control circuits 914 can include one or more FETs 915coupled to current sensing resistors 917, and one or more operationalamplifiers 919 that provide control feedback and receive currentsetpoints from the FPGA 908. Including a plurality of the currentcontrol circuits 914 in parallel can spread and dissipate heat acrossthe respective FETs 915 of the current control circuits 917 so as toimprove current control precision and reliability. In typical examples,the pump diode 902A has a different forward voltage than the pump diode902B. Thus, the voltage drop across a FET will vary between pump diodeseries. The AC/DC power supply 906 can be situated to maintain asuitable FET voltage that corresponds to a constant or consistent heatdissipation. The associated electronic efficiency and reliability of thecurrent control circuits 914 is improved as heat dissipation across theFETs 915 is partitioned and limited. Furthermore, the current controlresponse characteristics of the current control circuits 917 thatcontribute to the overall response time of the optical outputs 901A,901B of the pump diodes 902A, 902B are improved, allowing shorter risetimes and fall times associated with the resistors R_(B), R_(C), R_(D),and higher digital modulation frequencies. The apportioning of currentwith the parallel current control circuits 914 also allows selection ofcurrent sensor resistor values for the current sensing resistors 917that are more accurate, further improving response characteristics ofthe current control circuits 914 and optical outputs 901A, 901B. Withfast sample rates from the DAC 910, and with the improved responsecharacteristics of the current control circuits 914, laser diode currentcan be switched or varied rapidly. In some examples, rise times and falltimes for the optical outputs 901A, 901B of less than or equal to 50 μs,20 μs, 10 μs, 5 μs, or 2.5 μs are achieved, including with shortmodulations periods, such as less than 100 μs, 50 μs, 20 μs, 10 μs, or 5μs.

In some embodiments, the FPGA 908 receives an analog signal from ananalog input 918 from an external source that has been passed through asignal conditioner and ADC (not shown) The external source, such as anautomated system, computer, computer memory or data file, manualcontrol, graphical user interface input, etc., is configured to providethe analog signal based on a desired a laser system power level. Thelaser system can then be pumped by the optical outputs 901A, 901B inorder to achieve the desired laser system power level. The FPGA 908 canalso receive a gate signal from a gate input 920 that can be associatedwith the analog signal and the external source providing the analogsignal. The gate signal is typically digital and can be configured toprovide on and off commands for the pump diodes 902A, 902B so as to turna corresponding laser system beam on and off. The gate signal and analogsignal can also be used to produce an arbitrary waveform for the opticaloutputs 901A, 901B. In typical examples, the analog signal and the gatesignal are coordinated so that a laser system beam is scanned across atarget to selectively heat and process material of the target atdifferent power levels and at different locations of the target. A pulseprofile from a pulse profile signal input 922 can also be coupled to theFPGA 908 so as to provide an external source to select various featuresof the laser system beam generated from the pump diodes 902A, 902B. Thepulse profile information can be stored in a memory locally or remotelyor provided as a signal from an external source. For example, differentrise times and fall times can be selected for the pump currents, alongwith laser system beam repetition rates, power levels, etc.

A fluence modulation signal is received from a fluence modulation input924 that is also coupled to the FPGA 908 and which can also becoordinated with the analog signal, gate signal, and pulse profile, orit can be separate. The fluence modulation signal can be provided tocorrect for a fluence deviation associated with the laser system beambeing delivered to the target. For example, the analog input may have alimited bandwidth, for example, due to the increased noise typicallyassociated with high frequency analog signals, or the bandwidth may beunsuitable in relation to the dynamics of other laser system components,such as a scanner, or the laser process being performed. The fluencemodulation signal can be used to compensate for the bandwidth-limitedanalog signal or corresponding bandwidth-limited laser systemperformance by digitally modulating the pump currents in order toachieve a desired fluence at the target during laser processing with thelaser system beam produced with the optical outputs 901A, 901B. Forexample, when a scanning speed decreases, the fluence modulation signalcan be received by the FPGA 908 and the FPGA 908 can direct themultiplexer 912 over the serial bus 916 to modulate so as to produce thedesired fluence correction at the target.

Having described and illustrated the principles of the disclosedtechnology with reference to the illustrated embodiments, it will berecognized that the illustrated embodiments can be modified inarrangement and detail without departing from such principles. Forinstance, elements of the illustrated embodiments can be implemented insoftware or hardware. Also, the technologies from any example can becombined with the technologies described in any one or more of the otherexamples. It will be appreciated that some procedures and functions suchas those described with reference to the illustrated examples can beimplemented in a single hardware or software module, or separate modulescan be provided. The particular arrangements above are provided forconvenient illustration, and other arrangements can be used.

In view of the many possible embodiments to which the principles of thedisclosed technology may be applied, it should be recognized that theillustrated embodiments are only representative examples and should notbe taken as limiting the scope of the disclosure. Alternativesspecifically addressed in these sections are merely exemplary and do notconstitute all possible alternatives to the embodiments describedherein. For instance, various components of systems described herein maybe combined in function and use. We therefore claim all that comeswithin the scope and spirit of the appended claims.

We claim:
 1. An apparatus, comprising: a 3D optical scanner configuredto direct a laser beam to a target along a scan path at a variable scanvelocity; and a zoom beam expander configured to adjust a collimatedwidth of the laser beam based on the variable scan velocity to vary aspot size at the target along the scan path to adjust a fluence at thetarget such that the fluence is within a predetermined range along thescan path.
 2. The apparatus of claim 1, wherein the zoom beam expanderincludes entrance group optics and exit group optics, wherein the exitgroup optics includes one or more optics configured move along anoptical axis of the zoom beam expander.
 3. The apparatus of claim 1,further comprising adjusting a digital modulation of a power level ofthe laser beam based on the variable scan velocity.
 4. An apparatus,comprising: a zoom beam expander configured to adjust a width of a laserbeam to provide the laser beam with a variable spot size at a target; ascanner configured to direct the laser beam to the target along a scanpath; and a digital modulator configured to digitally modulate acontinuous-wave power of the laser beam in relation to the variable spotsize to provide a fluence at the target within a predetermined fluencerange along the scan path.
 5. The apparatus of claim 4, wherein thelaser beam is directed to the target along a scan path at a variablescan speed and the digital modulation is adjusted so as to maintain thefluence at the target within the predetermined fluence range along thescan path.